Glass is generally heated at a high temperature of about 680° C. to 710° C. (in air) to strengthen an intensity thereof. Although a protective layer may be coated onto a heat shielding film of the glass to prevent oxidization thereof, the extra step increases process complexity.
Alternatively, a heat shielding material may be coated onto the glass after the high temperature strengthening process so that the heat shielding performance of the glass does not deteriorate. Note that if tempered glass is subjected to a temperature higher than 300° C., strain therein would be released, thus causing the glass to lose its toughness. Tungsten oxide film is a well known heat shielding film with IR reflexivity. Tungsten oxide films are generally formed at a temperature above 500° C., and therefore, it is not suitable for tungsten oxide films to be incorporated into a tempered-glass manufacturing process.
A commercially available heat shielding glass is mainly a low radiation glass with single layer or double layer of silver, which is formed by sputtering silver, dielectric, and a protective film on the glass under a vacuum environment.
Therefore, the silver coating must be sealed between two pieces of glass filled with inert gas to prevent oxidation. However, if the inert gas leaks, the heat shielding performance will be negated and replacement of the gas assembly will be required.
Accordingly, a low-cost, highly stable IR reflective film which can be processed by a lower temperature is required.